The present invention is related to a rolling bearing unit with a rotational speed sensor, which is utilized to rotatably support a road wheel with reference to a suspension apparatus while detecting the rotational speed of the road wheel.
The road wheel is rotatably supported by a rolling bearing unit with reference to a suspension apparatus. In addition, the rotational speed of the road wheel must be detected in order to control an anti-lock braking system (ABS) and traction control system (TCS). Accordingly, recently the rolling bearing unit with rotational speed sensor, that is the rolling bearing unit having a rotational speed sensor installed therein, is broadly used to rotatably support the road wheel while detecting the rotational speed of the road wheel.
Japanese Utility Model Publication JITSUKAI HEI No. 7-31539 discloses one example of the prior art structures of the rotational speed sensor, which is also referred to as rpm detector in this specification, for use in such an object. An object of this publication is to provide a rolling bearing unit with rotation speed sensor wherein it is possible to take out only the rotation speed sensor from the hub cap for exchange and maintenance, to make short the axial size of the bearing unit, and to stabilize the sensor performance.
The rolling bearing unit of this publication comprises an inner ring member 202 (see FIGS. 77-79) onto the outer peripheral surface of which a pulser ring 204 is fixed fitted, the inner ring member 202 being fitted to a hub 201 at its end, and pressed by a nut 203 for fixing, an outer ring member 205 to which a hub cap 209 is attached, the hub cap 209 having a bottomed recess portion 209a enclosing the nut 203, a flanged portion 209b extending radially outward from the end of the bottomed recess portion 209a, an engagement portion 209c, and a cylindrical portion 209d.
The engagement portion 209c is formed at the end of the flanged portion 209b to abut the end face of the outer ring member 205. The cylindrical portion 209d extends axially from the engagement portion 209c to be fitted into the end of the outer ring member 205.
Removably fixed to the flanged portion 209b of the hub cap 209 is a sensor mount member 211 to which a rotation member detecting sensor 210 is integrally connected. The sensor mount portion 211 is positioned in the stepped space 214 defined by the bottomed recess portion 209a and the flanged portion 209b.
The inner ring member 202 has a mount portion 201a for fixing a road wheel, and a raceway 202a on its peripheral surface, and functions as a rotating shaft.
The outer ring member 205 has a mount portion 205a for connecting to a vehicle body, and a raceway on its inner peripheral surface. Rolling members are provided between the hub 201 and the outer ring member 205. Provided at one end of the hub is a pulser ring 204 which faces the rotation number detection sensor 210 with a slight clearance between them, and is fitted onto the outer peripheral surface of the inner ring member 202.
In this structure, a pair of bolts and nuts 12, 13 are used to securely fix a sensor 10 to a cover 9 of the rolling bearing unit (see e.g. FIG. 3 of the publication). This step is carried out in the assembling site of the rolling bearing unit with rotational speed sensor but inconvenient to need a long process time. In addition, the disengagement and engagement of the bolts and nuts for repairing the rotational speed sensor in the rolling bearing unit are also troublesome. This leads to cost-up in the production and repair.
U.S. Pat. No. 4,946,295 which is incorporated in the present specification by reference, discloses another example of the bearing unit with rpm detector where the sensor is easily-engaged and disengaged with and from the bearing unit for easy inspection and repair. No special tool is used to install the sensor at the end of the stationary outer ring. However, no seal device is installed in this structure to protect the encoder and sensor from outside. Specifically, the seal ring 10 in this structure is used for isolating the space for installing the rolling members 3 from outside, but not for isolating the encoder and sensor from outside. Accordingly, for example, when it rained, water drops may be kept attached to the clearance between the encoder 19 and sensor 8, which may lead to damages of the encoder and/or sensor if the automobile is started with the attached water drops frozen.
JP Patent Publication TOKUKAI HEI No. 9-1964945 discloses another example of the bearing unit with rpm detector, where the holder 26 with the sensor 12a embedded therein can be easily installed and removed with respect to the cover 23 fixed to the outer ring 2a without any special tool. However, some improvements are required in assembling the bearing unit with rpm detector. Specifically the cylindrical support body 27 must be placed in alignment with the holder 26 in phase in a circumferential direction. Therefore, the holder must often be rotated inside the cylindrical support body, but due to the presence of the elastically compressed O-ring on the cylindrical support body, the force to rotate the holder is substantially large to easily worsen the assembly performance of the bearing unit with rpm detector. In addition to the assembly performance, the performance of the rotational speed sensor must be taken into consideration with respect to the installation of the holder into the cover of the bearing unit.
The mechanism of the rotational speed sensor is detailed later referring to FIGS. 73 to 76.